Photo-Fries rearrangement phenyl acetate

If the photo-Fries reaction would occur via a concerted mechanism, the absence of solvent should be of minor importance for the formation of rearranged products. However, conclusive evidence supporting the radical pair mechanism arises from the experiments carried out with phenyl acetate (10) in the vapor phase. The major product in the irradiations of 10 is phenol (13), which accounts for 65% of the photoproducts. Under these conditions, less than 1% of ortho -hydroxyace-tophenone (11) appears to be formed [19,20]. Conversely, when a high cage effect is expected, as in rigid matrixes (i.e., polyethylene), the result is completely different, and phenol is practically absent from the reaction mixtures [29]. In the intermediate situation (liquid solution), both rearranged products and phenol are formed in variable amounts depending on solvent properties. These observations... 

Ramamurthy and coworkers studied the photo-Fries rearrangement of phenyl acetate and phenyl benzoate and photo-Claisen rearrangement of allyl phenyl ether (Fig. 34) included in two types of zeolite (faujasites X and Y and pen-tasils ZSM-5 andZSM-11) [192], The photolysis was performed with the zeolite slurry in either hexane or iso-octane. One of the most remarkable observations is that the product distribution is altered within zeolites from that in isotropic solvent. Furthermore, while in solution, nearly a 1 1 mixture of ortho and para isomers 40 and 41 (Fig. 34) was obtained, within zeolites one is able to direct the photoreaction selectively toward either the ortho or the para products by conducting the reaction either within faujasites or pentasils, respectively (Fig. 34). 

Figure 34 Photo-Fries rearrangement of phenyl acetate and phenyl benzoate, and photo-Claisen reaction of allyl phenyl ether in solution and within zeolites.

The photo-Fries rearrangement of phenyl acetate in aqueous solution in the presence and absence of B-cyclodextrin has been reexamined. In aqueous solution a mixture of phenol and the ortho and para isomers of hydroxyacetophenone is produced. When 3-cyclodextrin is present the quantum efficiency of formation of phenol and of the ortho product is increased. It is suggested that the enhanced photochemical yield of the ortho product reflects the less polar environment of the cyclodextrin cavity while the increased quantum yield of phenol formation reflects the availability of abstractable hydrogen within the cyclodextrin cavity. 

Suau, R., Torres, G., and Valpuesta, M. 1995. The photo-Fries rearrangement of 2,5-disubstituted phenyl acetates. Tetrahedron Lett. 36 1311-1314. 

Klan [56] described the photo-Fries rearrangement of phenyl acetate (37) under the action of microwaves and when irradiated with an electrodeless discharge lamp (EDL) (Chapter 19 of this book). The reaction provides two main products, 2- and 4-hydroxyacetophenone (Scheme 5.13 38 and 39, respectively). Product distributions are given in Table 5.3. 

Also obtained by UV light irradiation of phenyl acetate (photo-Fries rearrangement),... 

KW photo Fries rearrangement phenyl acetate, hydroxyacetophenone ... 

Photodecarboxylation in the presence of photocatalysts such as TiOj has also been studied. For example, the photodegradation of (4-chloro-2-methylphenoxy)acetic acid, a herbicide, in an aqueous solution of TiOj involves elimination of carbon dioxide from the initially formed radical species on the catalyst surface. The templating of carboxyHc acids with polyethylene films has been found to enhance the photodecarboxylation at the expense of the photo-Fries rearrangement in simple aryl esters such as phenyl and 1-naphthyl esters." ... 

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